The present invention relates generally to boat hoists and more particularly to a boat hoist employing a platform which is movable on an inclined plane to raise and lower the boat.
Mechanical hoists are commonly employed for elevating motor boats, launches, sailboats, pontoons, and other relatively small water craft out of the water when not in use so that they will not be buffeted by the wind and waves and knocked against an adjacent pier or dock, which can result in damage to the boat.
Examples of prior art hoists of the general type herein concerned are disclosed in the following U.S. Patents:
U.S. Pat. No. 4,109,896 describes a hoist having a scissor type lifting mechanism;
U.S. Pat. No. 4,401,335 describes a boat hoist including a vertically movable platform;
U.S. Pat. No. 3,697,048 describes a boat hoist having an arcuate lifting member positioned beneath the bow and stern portions of the boat;
U.S. Pat. No. 4,279,565 describes a hoisting apparatus having a sling type arrangement;
U.S. Pat. No. 4,022,027 describes a lifting frame including a winch for raising the boat above a freeze zone of a body of water;
U.S. Pat. No. 4,236,859 describes a mobile hoist including loading slings;
U.S. Pat. No. 4,391,550 describes a boat lift having opposed flotation tanks and a gunnel support system;
U.S. Pat. No. 4,027,492 describes a transportable boat lift including a collapsible framework;
U.S. Pat. No. 3,895,592 describes a boat lift which includes a float of polyurethane material;
U.S. Pat. No. 3,675,258 discloses a dock-mounted boat hoist which includes a scissor-type extensible and retractable arm assembly;
U.S. Pat. No. 3,220,196 discloses a boat dock which is used to raise boats from and lower boats into the water; and
U.S. Pat. No. 4,072,119 discloses a vertical raising boat lift.
While, as indicated above, there are numerous devices for lifting or hoisting boats in and out of the water, none discloses incorporating a platform movable on an inclined plane to provide a mechanical advantage in the lifting and lowering arrangement, even though the principle of using an inclined plane for mechanical advantage is well known, for example, as long ago as 1925, in an automobile hoist as shown in U.S. Pat. No. 1,537,800.